Difference between revisions of "2009 AMC 12A Problems"
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Let <math>p(x) = x^3 + ax^2 + bx + c</math>, where <math>a</math>, <math>b</math>, and <math>c</math> are complex numbers. Suppose that | Let <math>p(x) = x^3 + ax^2 + bx + c</math>, where <math>a</math>, <math>b</math>, and <math>c</math> are complex numbers. Suppose that | ||
− | <center>p(2009 + 9002\pi i) = p(2009) = p(9002) = 0</center> | + | <center><math>p(2009 + 9002\pi i) = p(2009) = p(9002) = 0</math></center> |
What is the number of nonreal zeros of <math>x^{12} + ax^8 + bx^4 + c</math>? | What is the number of nonreal zeros of <math>x^{12} + ax^8 + bx^4 + c</math>? |
Revision as of 01:25, 20 August 2012
Contents
[hide]- 1 Problem 1
- 2 Problem 2
- 3 Problem 3
- 4 Problem 4
- 5 Problem 5
- 6 Problem 6
- 7 Problem 7
- 8 Problem 8
- 9 Problem 9
- 10 Problem 10
- 11 Problem 11
- 12 Problem 12
- 13 Problem 13
- 14 Problem 14
- 15 Problem 15
- 16 Problem 16
- 17 Problem 17
- 18 Problem 18
- 19 Problem 19
- 20 Problem 20
- 21 Problem 21
- 22 Problem 22
- 23 Problem 23
- 24 Problem 24
- 25 Problem 25
Problem 1
Kim's flight took off from Newark at 10:34 AM and landed in Miami at 1:18 PM. Both cities are in the same time zone. If her flight took hours and
minutes, with
, what is
?
Problem 2
Which of the following is equal to ?
Problem 3
What number is one third of the way from to
?
Problem 4
Four coins are picked out of a piggy bank that contains a collection of pennies, nickels, dimes, and quarters. Which of the following could not be the total value of the four coins, in cents?
Problem 5
One dimension of a cube is increased by , another is decreased by
, and the third is left unchanged. The volume of the new rectangular solid is
less than that of the cube. What was the volume of the cube?
Problem 6
Suppose that and
. Which of the following is equal to
for every pair of integers
?
Problem 7
The first three terms of an arithmetic sequence are ,
, and
respectively. The
th term of the sequence is
. What is
?
Problem 8
Four congruent rectangles are placed as shown. The area of the outer square is times that of the inner square. What is the ratio of the length of the longer side of each rectangle to the length of its shorter side?
![[asy] unitsize(6mm); defaultpen(linewidth(.8pt)); path p=(1,1)--(-2,1)--(-2,2)--(1,2); draw(p); draw(rotate(90)*p); draw(rotate(180)*p); draw(rotate(270)*p); [/asy]](http://latex.artofproblemsolving.com/4/f/8/4f8d08abd119d663ad6630516ebc1b3bd784727e.png)
Problem 9
Suppose that and
. What is
?
Problem 10
In quadrilateral ,
,
,
,
, and
is an integer. What is
?
![[asy] unitsize(4mm); defaultpen(linewidth(.8pt)+fontsize(8pt)); dotfactor=4; pair C=(0,0), B=(17,0); pair D=intersectionpoints(Circle(C,5),Circle(B,13))[0]; pair A=intersectionpoints(Circle(D,9),Circle(B,5))[0]; pair[] dotted={A,B,C,D}; draw(D--A--B--C--D--B); dot(dotted); label("$D$",D,NW); label("$C$",C,W); label("$B$",B,E); label("$A$",A,NE); [/asy]](http://latex.artofproblemsolving.com/5/7/0/570b698fea7c6d66beab04dd6aee44dd24f2b6c1.png)
Problem 11
The figures ,
,
, and
shown are the first in a sequence of figures. For
,
is constructed from
by surrounding it with a square and placing one more diamond on each side of the new square than
had on each side of its outside square. For example, figure
has
diamonds. How many diamonds are there in figure
?
![[asy] unitsize(3mm); defaultpen(linewidth(.8pt)+fontsize(8pt)); path d=(1/2,0)--(0,sqrt(3)/2)--(-1/2,0)--(0,-sqrt(3)/2)--cycle; marker m=marker(scale(5)*d,Fill); path f1=(0,0); path f2=(0,0)--(-1,1)--(1,1)--(1,-1)--(-1,-1); path[] g2=(-1,1)--(-1,-1)--(0,0)^^(1,-1)--(0,0)--(1,1); path f3=f2--(-2,-2)--(-2,0)--(-2,2)--(0,2)--(2,2)--(2,0)--(2,-2)--(0,-2); path[] g3=g2^^(-2,-2)--(0,-2)^^(2,-2)--(1,-1)^^(1,1)--(2,2)^^(-1,1)--(-2,2); path[] f4=f3^^(-3,-3)--(-3,-1)--(-3,1)--(-3,3)--(-1,3)--(1,3)--(3,3)-- (3,1)--(3,-1)--(3,-3)--(1,-3)--(-1,-3); path[] g4=g3^^(-2,-2)--(-3,-3)--(-1,-3)^^(3,-3)--(2,-2)^^(2,2)--(3,3)^^ (-2,2)--(-3,3); draw(f1,m); draw(shift(5,0)*f2,m); draw(shift(5,0)*g2); draw(shift(12,0)*f3,m); draw(shift(12,0)*g3); draw(shift(21,0)*f4,m); draw(shift(21,0)*g4); label("$F_1$",(0,-4)); label("$F_2$",(5,-4)); label("$F_3$",(12,-4)); label("$F_4$",(21,-4)); [/asy]](http://latex.artofproblemsolving.com/d/2/4/d24a6830ee3382e3945990d8af2e9e00ba14c85e.png)
Problem 12
How many positive integers less than are
times the sum of their digits?
Problem 13
A ship sails miles in a straight line from
to
, turns through an angle between
and
, and then sails another
miles to
. Let
be measured in miles. Which of the following intervals contains
?
Problem 14
A triangle has vertices ,
, and
, and the line
divides the triangle into two triangles of equal area. What is the sum of all possible values of
?
Problem 15
For what value of is
?
Note: here .
Problem 16
A circle with center is tangent to the positive
and
-axes and externally tangent to the circle centered at
with radius
. What is the sum of all possible radii of the circle with center
?
Problem 17
Let and
be two different infinite geometric series of positive numbers with the same first term. The sum of the first series is
, and the sum of the second series is
. What is
?
Problem 18
For , let
, where there are
zeros between the
and the
. Let
be the number of factors of
in the prime factorization of
. What is the maximum value of
?
Problem 19
Andrea inscribed a circle inside a regular pentagon, circumscribed a circle around the pentagon, and calculated the area of the region between the two circles. Bethany did the same with a regular heptagon (7 sides). The areas of the two regions were and
, respectively. Each polygon had a side length of
. Which of the following is true?
Problem 20
Convex quadrilateral has
and
. Diagonals
and
intersect at
,
, and
and
have equal areas. What is
?
Problem 21
Let , where
,
, and
are complex numbers. Suppose that

What is the number of nonreal zeros of ?
Problem 22
A regular octahedron has side length . A plane parallel to two of its opposite faces cuts the octahedron into the two congruent solids. The polygon formed by the intersection of the plane and the octahedron has area
, where
,
, and
are positive integers,
and
are relatively prime, and
is not divisible by the square of any prime. What is
?
Problem 23
Functions and
are quadratic,
, and the graph of
contains the vertex of the graph of
. The four
-intercepts on the two graphs have
-coordinates
,
,
, and
, in increasing order, and
. The value of
is
, where
,
, and
are positive integers, and
is not divisible by the square of any prime. What is
?
Problem 24
The tower function of twos is defined recursively as follows: and
for
. Let
and
. What is the largest integer
such that
![\[\underbrace{\log_2\log_2\log_2\ldots\log_2B}_{k\text{ times}}\]](http://latex.artofproblemsolving.com/3/0/c/30ce227e6c3bfc6b946422c508d8e508f9b940bf.png)
is defined?
Problem 25
The first two terms of a sequence are and
. For
,
![\[a_{n + 2} = \frac {a_n + a_{n + 1}}{1 - a_na_{n + 1}}.\]](http://latex.artofproblemsolving.com/d/f/6/df68c0d3181ac4b7e48b2b812c37cd27f7efaf30.png)
What is ?